THIS Sunday, the lectionary returns to Mark’s Gospel, to a filleted version of 7.1-23. If left as a whole, it is a plain-speaking passage. Jesus had very little to say about homosexuality, nuclear weapons, and other modern issues. Yet, here he alludes to the natural process of defecation. Of course, the lectionary has cut that bit (v.19).

Jesus is easier to honour as Lord, it seems, when he is as far removed as possible from the reality of ordinary, common humanity. We like to depict him with angelic blue eyes, softly waving hair, flowing robes, infinite patience. God forbid that we should have a Saviour with bad skin, knock knees, or a short fuse.

In Umberto Eco’s novel The Name of the Rose, Jorge of Burgos wanted the world to be purged of laughter because he considered it an affront to God’s dignity, a display of the lowest part of our human nature. Human nature craves concealment of what we truly are (Genesis 3.7). Fig leaves are big: they need to be, to hide all that we would rather conceal from God.

As filleted, the Gospel tackles the Lord’s teaching on “defilement”. Thanks to modern medicine, humankind has gained knowledge about processes of disease transmission. But, for most of our existence, we have made do with unscientific categories like “dirt”, “germs”, or “humours”. Before the modern era, people knew little about the processes of illness; so it was easy to confuse correlation with causation.

My Cambridge college’s third founder, John Caius, was a 16th-century physician. He built the court that bears his name and has one side open to the elements, to maximise healthy air flow. Tudor Cambridge must have been a dirty, reeking place, especially so close to the river. But it was vermin, not air, that had spread the Black Death in the time of our first founder, Edmund Gonville.

People often think of Jewish purity rules (kashrut) as a form of proto-hygiene, as if God’s ancient people had somehow discovered that dirty hands could transmit infection, or lead to ingestion of pathogens. In fact, those rules functioned more as a system of classification, to categorise foodstuffs and prevent contamination through bringing fundamentally different kinds of thing (such as milk and meat) into contact.

Physical stuff, Jesus says, cannot defile us through our eating of it or, by extension, our touching of it (Luke 8.43-48). What defiles us is what is part of us, what stays with us even when we try to turn our backs on it. We may banish foul speech, foul conduct from our actions through monitoring, and self-control. But we cannot fully govern our instincts and appetites.

One way of understanding this teaching is to draw a contrast between the physical and moral universes. Food belongs to the realm of the physical, which is less important than the moral, or — in the case of Christianity — spiritual. Food is not of itself evil. Outside the rules of kashrut, it can corrupt us, or make us impure, only by the will or intention governing our act of eating.

But, when we look at the things that come out of a person — the things that do corrupt — there is no simple contrast between the physical, on the one hand, and the moral or spiritual on the other. The first things that Jesus mentions as corrupting certainly are physical: “fornication, theft, murder, adultery” (and slander) are all actions. But he goes on to include inclinations and attitudes: “avarice, wickedness, deceit, licentiousness, envy. . . pride, folly”.

Any wrong act diminishes us. But so, Jesus says, does an improper attitude on which we never act. Now, if even our uncontrollable thoughts “defile” us, we are beyond saving, beyond hope. But I do not think that Jesus is really making failures of us all. What he means by “defilement” depends on how we tackle the Greek verb.

Outside of the New Testament (and a single mention in the Apocrypha), this verb, koinoun, means “to make common, ordinary”. I want to incorporate this idea, balancing “defile” with the idea that things that come out of us make us “ordinary”. God intended for us to be the opposite of “common/ordinary”: sacred rather than profane (1 Corinthians 6.19). Sins of thought, action, or omission, though, drag us away from the spiritual realm, and leave us floundering, sinking back into the mud and slime from which God made us.

The Revd Dr Cally Hammond is Dean of Gonville and Caius College, Cambridge.